Rotary, positive displacement, sliding vane, power and hand pumps have been widely used. They are particularly useful for handling thin and viscous liquids. They are self-priming, for example, they prime themselves by pumping air and vapor at low speeds, such as on hand pump applications.
In some applications, it is desirable to empty the pump completely so that a different liquid can be handled with the same pump. This is a problem if there are any voids in the pump that do not drain quickly.
Most rotary sliding vane pumps seal at one point between the rotor and the housing. The rotor must be held in an exact location relative to the housing so that the liquid will not flow from the discharge back to the suction side of the pump. The pumps are more difficult and expensive to build because of the aforementioned seal and the close clearance required to effect it. Also, if any solids are present in the liquid, some will be caught in the small clearance space between the rotor and housing, leading to erratic operation and excessive wear.
Referring to FIG. 6, there is schematically illustrated a prior art sliding vane pump comprising a cylinder C having a closed end defined by an end wall E. A pump head (not shown) is fixable to the open end of the pump cylinder C and carries a bearing for rotatably supporting a rotor R. In the peripheral wall of the cylinder C are an opposed inlet port I and discharge port D. The inner peripheral wall of the pump cylinder C has the shape of an exact circle or a special cam shape. The rotor R is positioned in the cylinder C so that it nearly touches the inner wall of the cylinder C at the seal point P. This close clearance is desired so that a substantial amount of the fluid being pumped cannot pass the seal point P. In assembling the parts, the clearance is obtained by moving the rotor R with respect to the seal point P until the rotor just turns freely, then locking the rotor in position by securing the pump head that contains the bearing that controls the rotor position. This position is maintained for the life of the pump by pins (not shown) which are installed connecting the pump head with the pump cylinder C.
FIG. 7 schematically illustrates another prior art sliding vane pump. In this pump, the inlet port I and the discharge port D are circumferentially spaced from each other a distance such that a pair of the vanes V sealingly contacts the inner wall of the pump cylinder C between the discharge port D and the inlet port I. It is not necessary to maintain a close clearance between the rotor R and the inner wall of the pump cylinder C. However, it is necessary to position the leading edge of the discharge port D precisely with respect to the trailing edge of the inlet port I to avoid binding of the pump with a non-compressible fluid.
A disadvantage of these prior art sliding vane pump designs is that the rotors R are of circular design with an open center. This design traps in the rotor the fluid being pumped so that the pump cannot be drained quickly. It is desired that a pump be capable of being drained quickly so that the pump can be used to pump different fluids, for example, so that the same pump can be moved from one drum to another.
U.S. Pat. No. 3,700,363 discloses not a pump, but rather, a rotary sliding vane-type hydraulic motor in which the rotor has longitudinal grooves between the vane support flanges. The rotor is supported by bearings at its opposite axial ends so that it is rotatable about a fixed axis. There are many differences between pumps and motors even though, superficially speaking, a hydraulic motor can be considered to be a pump run backward. For example, the emphasis in pumps is on volumetric efficiency, whereas the emphasis in motors is on torque efficiency. Pumps operate in one direction in a given installation, whereas motors are required to reverse their direction of rotation. Because of these and related factors, a design that is completely acceptable in a hydraulic motor may operate poorly as a pump, and vice versa. Thus, the internal design features of hydraulic pumps and motors can be widely different from each other.